Fuel cell



June 1964 w. E. TRAGERT ETAL 3,138,490

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June 23, 1964- w TRAGERT ETAL 3,138,490

FUEL CELL Original Filed Feb. 28, 1961 2 Sheets-Sheet 2 Robert LFw/rndn,Ralph 13:. Carter,

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United States Patent 3,138,490 FUEL CELL William E. Tragert, Scotia,Robert L. Fnilman, Schenectady, and Ralph E. Carter, Colonic, N.Y.,assignors to General Electric Company, a corporation of New YorkContinuation of application Ser. No. 92,356, Feb. 28, 1961. Thisapplication Sept. 30, 1963, Ser. No. 312,710 13 Claims. (Cl. 13686) Thisinvention relates to fuel cells and more particularly to hightemperature fuel cells in which the electrolyte is solid and theelectrodes are in the liquid state during cell operation.

This application is a continuation of application Serial No. 92,356,filed February 28, 1961, now abandoned, and assigned to the sameassignee as the present application. In copending application Serial No.92,354, filed February 28, 1961, and assigned to the same assignee asthe present application, there is disclosed and claimed a fuel cell witha silver cathode, a solid stabilized zirconia electrolyte, and an anodeof porous carbonaceous material.

Where electrical energy is generated from the eat of chemical reactions,a fuel is generally oxidized by air and the chemical energy of the fuelis converted into heat and mechanical energy. This heat and mechanicalenergy is then used in gas turbines or steam turbines connected toconventional dynamoelectric generators to provide the electrical energyneeded. It is estimated that the overall elficiency of this conversionis less than 50 percent.

In order to avoid inefiiciency in this type of electricity generation,it has been proposed to employ fuel cells to convert the chemical energyof the fuel directly into electrical energy Without the conversion ofthe energy of the fuel into heat and mechanical energy. While carbonfossil fuels would be desirable in fuel cells, they are not readilybrought into a form suitable for electrochemical reaction. For example,coal poisons the electrodes of a fuel cell by its chemical impurities. Afurther problem is the requirement for a suitable electrolyte for thesuccessful operation of such a cell.

High temperature fuel cells would be advantageous to provide a lowvoltage direct current power source on a continuous basis. Such cellsshould employ preferably a carbon fuel, exhibit stability and efficiencyand be low in cost. These cells would have application in variouschemical process industries, such as the manufacture of aluminum and theelectro-refining of copper. Furthermore, the operation of direct currentmotors could be accomplished with these cells. Waste heat can beemployed effectively to operate the cells.

It is an object of our invention to provide a high temperature fuel cellwhich employs a carbon fuel, exhibits stability and efficiency and islow in cost.

It is another object of our invention to provide a fuel cell operable athigh temperatures in the range of 1000 C. to 1200 C.

It is another object of our invention to provide a fuel cell whichemploys electrodes in liquid state during operation.

It is a further object of our invention to provide a high temperaturefuel cell which includes a metallic, carbon solvent anode.

It is a still further object of our invention to provide a hightemperature fuel cell which employs a solid electrolyte.

3,138,490 Patented June 23, 1964 ice In carrying out our invention inone form, a high temperature fuel cell employs a silver electrode, asecond electrode selected from the group consisting of iron saturatedwith carbon and cobalt-tin saturated with carbon, the electrodescharacterized by being in liquid state during cell operation at hightemperatures, a solid stabilized zirconia electrolyte positioned betweenand in direct contact with said electrodes, means for supplying agaseous oxidant to said silver electrode, and means for supplying acarbon fuel to said second electrode.

These and various other objects, features, and advantages of theinvention will be better understood from the following description takenin connection with the accompanying drawing in which:

FIGURE 1 is a sectional view of a high temperature fuel cell embodyingour invention;

FIGURE 2 is a sectional view of a modified high temperature fuel cell;

FIGURE 3 is a sectional view of the fuel cell of FIG- URE 1 inoperation;

FIGURE 4 is a sectional view of another modified high temperature fuelcell; and

FIGURE 5 is a sectional view of a further modified high temperature fuelcell.

In FIGURE 1, a high temperature fuel cell is shown generally at 10 whichcomprises a first open container 11, for example, of alumina or carbonin which is positioned a second container 12 of solid stabilizedzirconia, the cell electrolyte. A metallic, carbon solvent electrode 13selected from the group consisting of iron saturated with carbon andcobalt-tin saturated with carbon is positioned in container 11 and is indirect contact with container 12. A silver electrode 14 is positioned insecond container 12. A lead 15, such as of carbon, contacts electrode 13by being inserted therein while a lead 16, such as of stainless steel,contacts electrode 14 in a similar manner. One end of lead 16 isinserted in the silver electrode and the other end is connected toapparatus (not shown) being operated by the cell. Lead 16 can be encasedby insulation 17. The free end of lead 15 is connected in a similarmanner to the same apparatus to complete the circuit from cell 10.Carbon saturation of anode 13 is maintained by supplying a carbon fuelthereto. Such means are shown by car bon lead 15 which dissolves whileproviding electrical contact to the anode. Means are provided forsupplying a gaseous oxidant in the form of air or oxygen to silverelectrode 14. For example, a tube 18 of zirconia, alumina or stainlesssteel is inserted into electrode 14 and connected to an oxidant supply(not shown).

In FIGURE 2, a modified high temperature fuel cell is shown which isidentical with the cell shown in FIG- URE 1 with the exception that analumina or a carbon cover 19 closes container 11. A port, valve, or line(not shown) is provided to remove carbon monoxide during cell operationfrom electrode 13. The closed cell is advantageous in that it isleakproof.

We discovered that an efficient, stable fuel cell could be constructedand operated in the temperature range of 1000 C. to 1200 C. to provide alow voltage direct current power source. We found that a preferredcathode was silver to which an oxidant was supplied during celloperation. Our development disclosed further that a metallic, carbonsolvent electrode provided an anode for the cell. Of the materialstested, we found that the group consisting of iron saturated with carbonand cobalt-tin saturated with carbon produced a satisfactory anode. The

electrodes were an iron carbon eutectic alloy which contained 4.3 weightpercent carbon and a cobalt-tin eutectic alloy which was saturated withcarbon. We tested also nickel-manganese, nickel-copper, andchromium-antimony, all saturated with carbon. These materials did notappear as suitable for use in such a fuel cell. Both cell electrodes arecharacterized by being in liquid state during cell operation at hightemperatures. \Ve found that a carbon lead could be inserted into theanode while a stainless steel lead could be inserted in the silverelectrode. An alumina, zirconia or stainless steel tube inserted in thesilver electrode provided oxygen or air to the silver in molten stateduring cell operation.

Solid, stabilized zirconia is an oxygen ion transport medium which canbe used as the electrolyte in such a high temperature fuel cell.Stabilized zirconia is a compound with a cubic crystal structureconsisting of zirconia to which is added calcium oxide, yttrium oxide,or mixed rare earth oxides. Substantially pure zirconia, that is acompound with a monoclinic structure which is not stabilized by theaddition of the above oxides, experiences volume changes when cycledthermally with resultant shattering of the material. Furthermore,substantially pure zirconia is not a low resistance ionic conductor.Stabilized zirconia is resistant to large volume changes upon thermallycycling and hence is mechanically stable. Additionally, stabilizedzirconia serves as an oxygen ion transport medium by virtue of the anionvacancies generated in the zirconia structure upon cationic substitutionof calcium, yttrium or rare earth metals for zirconium.

Each substitution of a divalent calcium ion for a tetravalent zirconiumion results in a charge unbalance in the crystal that is redressed bythe absence of a divalent oxygen ion from a normally occupied anion sitein the lattice. The concentration of vacancies is thus equal to theconcentration of calcium ions in the zirconia. Since the movement of anoxygen ion vacancy through the lattice is the converse of an oxygen ionmovement in the opposite direction, a relatively high degree of oxygenmobility can be realized at fuel cell operating temperatures where theion-vacancy interchange occurs readily. A flux of oxygen through thestabilized zirconia lattice is effected by the establishment of anelectric field resulting from the chemical potential difference foroxygen existing across the crystal. The relatively good conductivity,coupled with chemical stability and strength of the stabilized zirconiaprovides a very satisfactory electrolyte for high temperature fuelcells.

In FIGURE 3 of the drawing, the operation of fuel cell in FIGURE 1 isshown. The operation of the fuel cell in FIGURE 2 is identical inoperation. Heat, such as waste heat, is supplied from a source (notshown) to raise the temperature of electrodes 13 and 14 of cell 10 inthe range of 1000 C. to 1200 C. The molten silver cathode is thensaturated with oxygen by bubbling air or oxygen through tube 18 intoliquid electrode 14. The reaction at the cathode-electrolyte interfaceis as follows:

(1) O+2e- O The oxygen ion moves through electrolyte 12 to combine withcarbon in accordance with the following reaction at theanode-electrolyte interface:

The electrons, which are given up at the anode are conducted throughlead to the apparatus (not shown) being operated while the oxygen at thecathode combines with the returning electrons. Carbon is added to anode13 to provide carbon saturation thereof. The carbon monoxide which isgenerated at the anode can be released to the atmosphere, used toprovide further heat for cell 10, or fed to a fuel cell employing carbonmonoxide as a fuel. In the fuel cell shown in FIGURE 2, the carbonmonoxide is released through a port, valve or line (not shown) andutilized in the same manner as in the fuel cell of FIGURE 1.

In FIGURE 4, another modified high temperature fuel cell is shown whichcomprises a solid stabilized zirconia electrolyte 20 in the form of ahollow tubular member, a silver electrode 21 in direct contact with theexterior surface of member 20, and an electrode 22 selected from thegroup consisting of iron saturated with carbon and cobalt-tin saturatedwith carbon in direct contact with the interior surface of member 20.The electrodes can be reversed with the silver electrode in directcontact with the interior surface of member 20 while the other electrodeis in direct contact with the exterior surface thereof. A lead 23 isattached to silver electrode 21 while a lead 24 is attached to the otherelectrode. The free ends of the leads are connected to apparatus (notshown) being operated by the cell. Means are provided for supplying agaseous oxidant in the form of air or oxygen to silver electrode 21. Forexample, a tube 25 connected to an oxidant supply (not shown) suppliesoxidant to electrode 21. Carbon fuel is supplied to the electrodeselected from the group consisting of iron saturated with carbon andcobalt-tin saturated with carbon. For example, an inlet line 28 sprays afinely divided carbonaceous material in an inert gas such as nitrogenthrough the cell to deposit the carbon on electrode 22. An outlet line29 removes the carbon monoxide formed at electrode 22 and the nitrogen.

In FIGURE 5, a further modified high temperature fuel cell is shownwhich comprises a solid stabilized zirconia electrolyte in the form of acontainer 25, a silver electrode 27 in direct contact with the exteriorsurface of container 26, and an electrode 28 selected from the groupconsisting of iron saturated with carbon and cobalt-tin saturated withcarbon positioned within the container 26. A lead 15 such as of carboncontacts electrode 28 by being inserted therein while a lead 23 isattached to silver electrode 27. The free ends of these leads are alsoconnected to appropriate apparatus (not shown). Carbon saturation ofanode 28 is maintained for example by dissolving partially carbon lead15 while the lead provides electrical contact thereto. A tube 25connected to an oxidant supply (not shown) supplies oxidant to electrode27.

In the operation of the fuel cell in FIGURE 4, heat, such as waste heat,is supplied from a source (not shown) to raise the temperature ofelectrodes 21 and 22 in the range of 1000 C. to 1200 C. The silverelectrode is saturated with oxygen which is supplied from tube 25.Carbon fuel is supplied to electrode 22 through inlet line 28 whilecarbon monoxide and nitrogen are removed through outlet line 29.Reactions 1 and 2 apply to the operation of this cell.

The operation of the fuel cell in FIGURE 5 is generally similar to theoperation of cell 10 in FIGURE 1. However, silver electrode 27 issaturated with oxygen which is supplied from tube 25. Reactions 1 and 2apply also to the operation of this cell.

A plurality of high temperature fuel cells were made in accordance withthe present invention. In Table I, in which these cells are identifiedby cell numbers 1 through 19, there is set forth for each cell its anodematerial, operating temperature, load voltage in volts, current densityin milliamperes, and operating time. During operation, each cellconsisted of a liquid iron saturated with carbon anode or a liquidcobalt-tin saturated with carbon anode as set forth in Table I, anoxygen-saturated liquid silver cathode, and a solid stabilized zirconiaelectrolyte positioned between and in direct contact with theelectrodes. Oxygen saturation of the cathode was achieved by bubblingoxygen through an alumina or stainless steel tube into the liquidsilver. The anode was positioned in a first container of alumina orcarbon while a second container of stabilized zirconia, the solidelectrolyte, was positioned in the first container. The anode was indirect contact with both containers. The cathode was positioned in thesecond container. Electrical leads were connected to both electrodes andpower generated by the cell was dissipated in a simple decade resistor.Carbon was added to the anode by dissolving partially its carbon lead.Each cell was heated to its operating temperature in a resistancefurnace.

While other modifications of this invention and variations thereof whichmay be employed within the scope of the invention have not beendescribed, the-invention is intended to include such that may beembraced within the following claims.

What We claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a fuel cell including an anode, the combination of a solidstabilized zirconia electrolyte, a silver cathode in direct contact withone surface of said electrolyte, said cathode characterized by being inliquid state during cell operation, and means for supplying a gaseousoxidant containing molecular oxygen to said silver cathode.

2. A fuel cell comprising a silver electrode, a second electrodeselected from the group consisting of iron saturated with carbon andcobalt-tin saturated with carbon, said electrodes characterized by beingin liquid state during cell operation at temperatures in the range of1000 C. to 1200 C., a solid stabilized zirconia electrolyte positionedbetween and in direct contact with said electrodes, means for supplyinga gaseous oxidant containing molecular oxygen to said silver electrode,means for supplying a carbon fuel to said second electrode, and meansfor excluding molecular oxygen from said second electrode during celloperation.

3. A fuel cell comprising a silver electrode, a second electrodeselected from the group consisting of iron saturated with carbon andcobalt-tin saturated with carbon, said electrodes characterized by beingin liquid state during cell operation at temperatures in the range of1000 C. to 1200 C., a solid stabilized zirconia electrolyte positionedbetween and in direct contact with said electrodes, means for supplyinga gaseous oxidant containing molecular oxygen to said silver electrode,said means comprising a tube inserted in said silver electrode, meansfor supplying a carbon fuel to said second electrode, and means forexcluding molecular oxygen from said second electrode during celloperation.

4. A fuel cell comprising a container, a silver electrode in saidcontainer, at second electrode selected from the group consisting ofiron saturated with carbon and cobalttin saturated with carbon withinsaid container, said electrodes characterized by being in liquid stateduring cell operation at temperatures in the range of 1000 C. to 1200C., a solid stabilized zirconia electrolyte positioned between and indirect contact with said electrodes, means for supplying a gaseousoxidant containing molecular oxygen to said silver electrode, means forsupplying a carbon fuel to said secondelectrode, and means for excludingmolecular oxygen from said second electrode during cell operation.

5. A fuel cell comprising a first container, a second containerconsisting of solid stabilized zirconia positioned within said firstcontainer, a silver electrode, a second electrode selected from thegroup consisting of iron saturated with carbon and cobalt-tin saturatedwith carbon, said electrodes characterized by being in liquid stateduring cell operation at temperatures in the range of 1000 C. to 1200C., one of said electrodes positioned in said first container and indirect contact with said second container, and the other of saidelectrodes in said second container, means for supplying a gaseousoxidant containing molecular oxygen to said silver electrode, means forsupplying a carbon fuel to said second electrode, and means forexcluding molecular oxygen from said second electrode during celloperation.

6. A fuel cell comprising a closed first container, 21 second containerconsisting of solid stabilized zirconia positioned within said firstcontainer, a silver electrode, a second electrode selected from thegroup consisting of iron saturated with carbon and cobalt-tin saturatedwith carbon, said electrodes characterized by being in liquid stateduring cell operation at temperatures in the range of 1000 C. to 1200C., one of said electrodes positioned in said first container and indirect contact with said second container, and the other of saidelectrodes in said second container, means for supplying a gaseousoxidant containing molecular oxygen to said silver electrode, means forsupplying a carbon fuel to said second electrode, and means forexcluding molecular oxygen from said second electrode during celloperation.

7. A fuel cell comprising a first container, a second containerconsisting of solid stabilized zirconia positioned within said firstcontainer, a silver electrode, an electrical lead contacting said silverelectrode, a second electrode selected from the group consisting of ironsaturated with carbon and cobalt-tin saturated With carbon, anelectrical lead contacting said second electrode, said electrodescharacterized by being in liquid state during cell operation attemperatures in the range of 1000 C. to 1200" C., one of said electrodespositioned in said first container and in direct contact with saidsecond container, and the other of said electrodes in said secondcontainer, means for supplying a gaseous oxidant containing mo lecularoxygen to said silver electrode, means for supplying a carbon fuel tosaid second electrode, and means for excluding molecular oxygen fromsaid second electrode during cell operation.

8. A fuel cell comprising a first container, a second containerconsisting of solid stabilized zirconia positioned Within said firstcontainer, a silver electrode, a stainless steel lead contacting saidsilver electrode, a second electrolyte selected from the groupconsisting of iron saturated with carbon and cobalt-tin saturated withcarbon, a carbon lead contacting said second electrode, said electrodescharacterized by being in liquid state during cell operation attemperatures in the range of 1000 C. to 1200 C., one of said electrodespositioned in said first container and in direct contact with saidsecond container, and the other of said electrodes in said secondcontainer, means for supplying a gaseous oxidant containing molecularoxygen to said silver electrode, and means for excluding molecularoxygen from said second electrode during cell operation.

9. A fuel cell comprising a container consisting of solid, stabilizedzirconia, an electrode selected from the group consisting of ironsaturated with carbon and cobalt-tin saturated with carbon within saidcontainer, a silver electrode in direct contact with the exteriorsurface of said container, said electrodes characterized by being inliquid state during cell operation at temperatures in the range of 1000C. to 1200 C., means for supplying a carbon fuel to said firstelectrode, means for excluding molecular oxygen from said firstelectrode during cell operation, and means for supplying a gaseousoxidant containing molecular oxygen to said silver electrode.

10. A fuel cell comprising a container consisting of solid stabilizedzirconia, an electrode selected from the group consisting of ironsaturated with carbon and cobalt-tin saturated with carbon within saidcontainer, a silver electrode in direct contact with the exteriorsurface of said container, said electrodes characterized by being inliquid state during cell operation at temperatures in the range of 1000C. to 1200 C., an electrical lead contacting said first electrode, anelectrical lead contacting said silver electrode, means for excludingmolecular oxygen from said first electrode during cell operation, meansfor supplying a carbon fuel to said first electrode, and means forsupplying a gaseous oxidant containing molecular oxygen to said silverelectrode.

11. A fuel cell comprising a hollow member consisting of solidstabilized zirconia, a silver electrode in direct contact with a surfaceof said member, a second electrode selected from the group consisting ofiron saturated with carbon and cobalt-tin saturated With carbon indirect contact with the opposite surface of said member, said electrodescharacterized by being in liquid state during cell operation attemperatures in the range of 1000 C. to 1200" C., means for supplying agaseous oxidant containing molecular oxygen to said silver electrode,means for supplying a carbon fuel to said second electrode, and meansfor excluding molecular oxygen from said second electrode during celloperation,

12. A fuel cell comprising a hollow member consisting of solidstabilized zirconia, a silver electrode in direct contact with theexterior surface of said member, and electrical lead contacting saidsilver electrode, a second electrode selected from the group consistingof iron saturated With carbon and cobalt-tin saturated with carbon indirect contact with the interior surface of said member, an electricallead contacting said second electrode, said electrodes characterized bybeing in liquid state during cell operation at temperatures in the rangeof 1000 C. to 1200 C., means for supplying a gaseous oxidant containingmolecular oxygen to said silver electrode, means for supplying a carbonfuel to said second electrode, and means for excluding molecular oxygenfrom said second electrode during cell operation.

13. In a fuel cell, in combination, a molten silver cathode, a moltenanode selected from the group consisting of iron saturated with carbonand cobalt-tin saturated with carbon, and a solid stabilized zirconiaelectrolyte disposed between and contacting opposed portions of saidcathode and said anode.

References Cited in the file of this patent UNITED STATES PATENTS569,591 Short Oct. 13, 1896 2,830,109 Iusti et al. Apr. 8, 19582,914,596 Gorin et al Nov. 24, 1959 OTHER REFERENCES Journal of theElectrochemical Soc., vol. 104, June 1957, pages 379-386.

1. IN A FUEL CELL INCLUDING AN ANODE, THE COMBINATION OF A SOLIDSTABILIZED ZIRCONIA ELECTROLYTE, A SILVER CATHODE IN DIRECT CONTACT WITHONE SURFACE OF SAID ELECTROLYTE, SAID CATHODE CHARACTERIZED BY BEING INLIQUID STATE DURING CELL OPERATION, AND MEANS FOR SUPPLYING A GASEOUSOXIDANT CONTAINING MOLECULAR OXYGEN TO SAID SILVER CATHODE.